DFFOO [JP][Yuri IW] Alphinaud HP poisoning the boss while it takes 999% less HP dmg w Vayne, Llyud
20This fight is actually a very interesting place to put Alphinaud besides Vayne.
Alphinaud counters Yuri's Intertwined Wills boss in multiple ways:
1. Party wide break immunity
Whenever the orb is at 0 the boss puts a doom debuff onto your party and also throws out a darkga++ in your face. Generally if you get broken, you take quite heavy dmg.
Since Alphinaud makes the entire party immune to break, you can straight up ignore the Doom debuff and take the orb attack as a mild breeze. He trivializes the orb mechanic entirely.
2. HP poisoning
While the boss takes 999% less HP dmg when adds are out at 3 different HP thresholds, HP poison does not take HP dmg factor into consideration, thus bypassing the entire dmg immunity.
Both Llyud and Vayne (both LD and BT does) provide a large amount of ATK up. With Vayne and Alphinaud constantly taking turns (but keep it under 6 consecutive turns, else there would be a field freeze to stop any form of BRV acquisition) the boss takes quite a lot of stacked up HP poison dmg. All 3 add phases alone adds up to around 10% and there is more outside of that.
3. 100% AoE, split and Splash dmg that you can choose
This is specifically directing at the friend Laguna BT debuff on the boss. It requires targetting to trigger it, but since the boss is practically immune to HP dmg it is quite inefficient to target the boss with a ST attack or a splash attack. Alphinaud can instead use his BRV++ to target the boss and still deal full dmg, or use his EX to trigger it with split dmg. When you want to focus down one of the adds though, you still have the option of the splash HP++ and energy drain. So he has all of the tools available for all of the situations presented here.
Using Vayne:
Technically using Vayne here is kinda against all odds - Too many breaks on adds equals instant turn rate and HP attacks from the skeletons; 6 consecutive turns means field freeze and unable to deal dmg, and Vayne has the S2-S2-LD-S2-S2-EX combo that can cause that. Realistically either you have to plan ahead on how to throttle or use EX/BT early when you still have the stacks to hit the brakes. It is just about counting. planning and learning how to stop, just like in his BT debut Lufenia+ with the flowers.
Vayne with Alphinaud:
Even though he requires more attention to play in this stage, the reward of successfully putting him with Alphinaud is quite satisfying. He gives the necessary ATK aura and consecutive turns for Alphinaud to thrive and in turn Alphinaud gives him the BRV gain, battery and BRV/HP dmg up that he craves as a Lv.80 character. This stage features an odd 30/90 reduction, both of which affect Vayne's DPS.
The same advantage that Alphinaud offers to Yda having easier time to break more enemies applies to Vayne. It is not in the sense that Vayne needs Alphinaud's help to break more people, it is more about other people having more opportunities of breaking the enemy when they recover from breaks with 0 BRV as a result of BRV sap, thus triggering more Vayne's BT follow-up.
Alas, they both pull through with flying colours. Combining with Laguna's BT debuff, they make quite a deadly combo.